As of 2015, there are no credible medical recommendations available regarding specific supplements for gaining weight. However, many fitness and nutrition sites such as Muscle & Fitness support the use of protein and meal replacement shakes as a method for gaining weight and muscle.
Eating calorie- and nutrient-rich foods is key when trying to gain weight, according to WebMD. People shouldn't simply eat more high-calorie foods with added sugar, fat and empty calories; rather, they should strive to eat frequent mini-meals that emphasize protein, vegetables, starch and healthy fat.
People who need to gain weight should focus on adding lean body weight or muscle mass, as opposed to body fat, according to the San Francisco Chronicle. Engaging in strength training sessions two to three times per week helps to prevent extra calories from accumulating as fat. Protein shakes are filling and helpful to supplement a healthy diet in combination with a strength training program. Protein powders can be blended with nut butters, yogurt, milk and fruit to maximize calorie intake.
Whey and casein protein powders are two of the most popular weight-promoting supplements used for increasing muscle, according to Muscle & Fitness. Both work to promote protein synthesis, or muscle building, when taken before or after a resistance training session. Creatine is another supplement commonly used for gaining weight and muscle mass, and it also helps with weight-lifting performance.